[Icom] Question about Icom IC-706MK2G SWR Meter

[Adam Farson]

Hi George,

From a look at the LPF board layout (Fig. 8-5, p. 11, IC-706MkIIG service
manual) the reflectometer transformerL33 is quite small, suggesting few
secondary turns. To ensure that the resulting low RF output voltage is well
above the offset voltage of the detector diodes, a reasonable RF power
throughput is required. This is probably the rationale for the 30W minimum
stated in the user manual.

Cheers for now, 73,
Adam VA7OJ/AB4OJ

-----Original Message-----
From: icom-admin@mailman.qth.net [mailto:icom-admin@mailman.qth.net]On
Behalf Of George, W5YR
Sent: Thursday, November 28, 2002 20:27
To: icom@mailman.qth.net
Subject: Re: [Icom] Question about Icom IC-706MK2G SWR Meter


Thanks for the detailed response, Bill - sorry if I came across as
sounding like I was doubting your word, but this is just something
really new to me. No demo required!  <:}

Very curious that so much output power would be required  for a valid
reading but perhaps our friend Adam, VA7OJ, can fill in the blanks.


73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
In the 57th year and it just keeps getting better!
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
K2 #489      Icom IC-765 #2349     Icom IC-756 PRO  #2121




----- Original Message -----
From: "Bill Archer" <bfarcher@attbi.com>
To: <icom@mailman.qth.net>
Sent: Thursday, November 28, 2002 8:50 PM
Subject: Re: [Icom] Question about Icom IC-706MK2G SWR Meter


> IC-706MKIIG Instruction Manual, page 38 near the top of the page on
the
> right hand side under  Measuring SWR..... (A) Spot
Measurement...."1)
> Confirm that the output power is over 30 W"
>
> or (B) Plot measurement......"1) Confirm that the output power is
over 30
> W"
>
> The BetterRF plug-in module "fools" the radio into thinking an
AT-180 is
> attached and generates a 10W CW signal to activate the AT-180 tuner.
On
> page 62 of the IC-706MKIIG manual under Specifications for the
AT-180
> while the Maximum input power is listed as 120 W the Minimum tuning
power
> is listed as 8 W.
>
> When I installed the rig in my van I assumed that with the BetterRF
module
> and the built-in SWR meter I could tune the High Sierra screwdriver
I had
> decided on.
> While the rig would  show a SWR of 1.2 or so using the BetterRF
module
> when switching to full power SSB transmission the SWR could be well
over
> 3:1.  Subsequently I installed an in-line cross-needle meter on the
dash
> to facilitate tuning the screwdriver. At low power(10W) the Icom
meter
> could show a 1:1 match only to have the meter go off scale at 100W.
>
> I hope this explains my  position George, if you would like a
> demonstration I would be glad to provide one.
>
> Bill in Plano
>
> "George, W5YR" wrote:
>
> > Bill, that is the first Icom I have ever heard of that required
more
> > than a watt or so for a valid SWR reading. My PRO puts out only
1.55
> > watts at min power setting and that is more than enough. Same with
765
> > and 430.
> >
> > Is this something specified in the manual or does yours just
happen to
> > work this way - maybe have a problem?
> >
> > Got me really curious . . .  <:}
> >
> > 73/72, George
> > Amateur Radio W5YR -  the Yellow Rose of Texas
> > In the 57th year and it just keeps getting better!
> > Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
> > K2 #489      Icom IC-765 #2349     Icom IC-756 PRO  #2121

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